1. Field of the Invention
The invention relates to a ball-grid array (BGA) IC packaging frame, and in particular to a ball-grid array IC packaging frame having supporting pads for preventing non-contact soldering and short circuits.
2. Description of the Related Art
A ball-grid array (BGA) IC packaging, a novel IC packaging with a large number of pins, is suitable for sub-micron ultra-large scale integrated circuits. The more complicated the functions of ICs, the higher the integration of transistor-based ICs. Generally, the conventional quad flat pack (QFP) and pin-grid array (PGA), which commonly only provide about 100-200 pins for each packaging, cannot handle with current complicated digital logic ICs. That is, the QFP and PGA cannot meet practical requirements at all.
Today, 64-bit microprocessor-based personal computers (PCs) have been widely utilized. The core logic circuits of a PC are electrically connected to a microprocessor, DRAMs serving as main memories and SRAMs serving as fast access memories thereof by a 64-bit bus. When the core logic circuits are manufactured into an IC chip, at least approximate 200 pins are required for a data bus and a address bus. If other control signals are taken into consideration, the total number of pins required are easily over 300. In this case, the BGA IC packaging can meet the requirement for a large number of pins.
A ball-grid array packaging substrate is constituted by a small-size printed circuit board (PCB) based on a printed circuit technique. As known by those skilled in the art, a die is automatically mounted on the substrate by a pick-and-place machine after wafer sawing. Then, the bonding pads of the dice are connected to the corresponding IO pads of the substrate with wires by a wire-bonding machine. Next, the die including the bonding pads and IO pads is encapsulated with a plastic molding compound by a molding machine. After the plastic cools, a solder reflow treatment is performed to form several hundreds of tin balls on the rear surface of the substrate. Since logic circuits contained in a current IC have more various functions and the operating frequency thereof already reaches several hundreds of MHz, more number of IO pads and shorter lengths of wires between a die and pines are required to perform IC packaging. Accordingly, the BGA IC packaging has been mainly and widely utilized for packaging high-integration and high-speed ICs in recent years. The BGA IC packaging has the following advantages.
(1) More IO pads can be provided.
(2) IC packages having small sizes are suitable for small-size equipment, such as notebooks.
(3) Ground bounce is greatly reduced, especially for high-speed circuits due to small inductance between induced by shorter wires.
(4) Tin balls are utilized to electrically connect a PCB, instead of conventional lead pins. Therefore, the problem of pins bent or shifted during delivery can be completely eliminated.
However, several disadvantages exist in the BGA IC packaging. Referring to FIG. 1, a bottom view of a BGA IC package 10 according to the prior art is shown. A plurality of ball-grid array tin balls 14 is formed on the rear surface of the conventional BGA IC package 10. Since the BGA IC package 10 is used in coordination with surface-mount technology (hereinafter referred to as SMT) where tin balls are utilized for connection with a PCB instead of pins, requirements for packaging become stricter. The SMT is a method to mount a BGA IC chip on a PCB. Then, a nitrogen solder reflow treatment is performed to melt the tin balls 14 beneath the BGA IC package 10, making the BGA IC and PCB knitted together to form a functional system. At this time, if the temperature-time curve of the nitrogen solder reflow treatment is not well-controlled, a short circuit between two adjacent tin balls as shown in FIG. 2 or non-contact soldering as shown in FIG. 3 will occur.
Referring to FIG. 4, a poor contact between a BGA IC 16 and a PCB 18 is shown. can be obviously seen from FIG. 4, non-contact soldering 20 and a short circuit 22 occur on a first end and a second end of the BGA IC 16 where the first end is higher than the second end, because of having no supports, such as pins in PGA, to support the BGA IC 16. This is a disadvantage of the BGA IC packaging.
Further more, in the SMT, the BGA IC 16 is mounted on the PCB 18 thereby to allow tin balls beneath the BGA IC 16 to connect corresponding tin solders which was spread on the surface of the PCB pads. How ever, the tin solders on the PCB will be dissipated if the BGA IC 16 is placed down from a higher position or the tin solders are easily squeezed if the BGA IC 16 is placed down form a lower position. Either will put the tin solders on the PCB in an inappropriate collapsed soldering condition, resulting in short circuits or non-contact soldering. Moreover, the PCB is easily warped by heat, causing being unable to be stably placed. This results in a poor yield.